CVE-2019-9785 in gitnote
Summary
by MITRE
gitnote 3.1.0 allows remote attackers to execute arbitrary code via a crafted Markdown file, as demonstrated by a javascript:window.parent.top.require('child_process').execFile substring in the onerror attribute of an IMG element.
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Analysis
by VulDB Data Team • 08/01/2023
The vulnerability identified as CVE-2019-9785 represents a critical remote code execution flaw in gitnote version 3.1.0 that stems from inadequate input validation and insecure rendering of markdown content. This vulnerability falls under the category of CWE-94, which describes "Improper Control of Generation of Code" and specifically relates to insufficient sanitization of user-supplied data. The flaw manifests when the application processes markdown files containing malicious payloads, particularly through the manipulation of HTML attributes within image elements. Attackers can exploit this vulnerability by crafting a specially formatted markdown file that includes a javascript: URI scheme within the onerror attribute of an img element, leveraging the window.parent.top.require('child_process').execFile function call to execute arbitrary system commands.
The technical implementation of this exploit relies on the application's failure to properly sanitize or escape user-provided content during markdown rendering. When gitnote processes a markdown file containing an img tag with a malicious onerror attribute, it fails to validate that the javascript: protocol within the attribute is legitimate or safe. The vulnerability specifically targets the application's handling of inline javascript execution within image error handlers, which should never be permitted in a secure content rendering environment. This type of attack vector demonstrates a classic cross-site scripting vulnerability that has been escalated to remote code execution through the application's use of node.js child_process module, allowing attackers to execute system commands with the privileges of the running application.
The operational impact of CVE-2019-9785 extends far beyond simple data theft or service disruption, as it provides attackers with complete system compromise capabilities. An attacker who successfully exploits this vulnerability can execute arbitrary commands on the target system, potentially leading to full system takeover, data exfiltration, or establishment of persistent backdoors. The vulnerability is particularly dangerous because it requires no authentication to exploit, making it a prime target for automated attacks and zero-day exploitation campaigns. The attack surface is broad since any user who can upload or import markdown files into the application becomes a potential vector for exploitation, and the impact is severe enough to warrant immediate remediation efforts. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under T1059 for Command and Scripting Interpreter, specifically targeting the execution of system commands through compromised applications.
Mitigation strategies for CVE-2019-9785 must address both the immediate vulnerability and broader security posture of the affected system. The primary remediation involves updating to a patched version of gitnote that properly sanitizes user input and prevents the execution of javascript within image attributes. Organizations should implement strict content validation policies that strip or escape all javascript protocols from user-supplied content, particularly within HTML attributes that can trigger event handlers. Additional defensive measures include implementing web application firewalls that can detect and block suspicious patterns in uploaded content, as well as deploying sandboxed environments for processing user-generated content. The vulnerability also highlights the importance of secure coding practices and input validation, particularly when dealing with rich text or markdown processing. Security teams should conduct comprehensive penetration testing to identify similar vulnerabilities in other applications that process user-supplied content, and implement automated scanning tools that can detect malicious patterns in uploaded files. Organizations should also consider implementing principle of least privilege for applications that process user content, limiting the system capabilities available to the application to reduce potential impact of successful exploitation.